Systems and methods for time optimization for silencing wireless devices in coexistence networks

ABSTRACT

Embodiments provide a communication device. A device comprises at least two dissimilar network technology subsystems, at least one subsystem of which is lower priority than at least another of the dissimilar subsystems. In some embodiments, a device is able to transmit a silencing frame during a transmission window within a lower priority technology network interval. A transceiver is able to calculate a transmission window to end by at least a duration of time to complete transmission of the silencing frame prior to the beginning of next immediate string of at least one higher priority network technology subsystem interval, and transmit a silencing frame during a lower priority technology network interval during the transmission window.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of and claims priority to U.S. patentapplication Ser. No. 13/748,083, filed Jan. 23, 2013. Said applicationis a Continuation of and claims priority to U.S. patent application Ser.No. 13/304,852, filed Nov. 28, 2011—now U.S. Pat. No. 8,886,140—which isa Continuation-in-Part of and claim priority to both U.S. Ser. No.12/251,187 filed on Oct. 14, 2008, issued Nov. 29, 2011 as U.S. Pat. No.8,068,871, and to U.S. provisional patent application Ser. No.61/426,628, filed Dec. 23, 2010, and entitled “System and method forSilencing Wireless Devices”. U.S. Ser. No. 12/251,187 also claimspriority to U.S. provisional patent application Ser. No. 61/016,062,filed Dec. 21, 2007, and entitled “Time Optimization for Silencing ofWireless Devices in Coexistence Networks.” This application is relatedto U.S. patent application Ser. No. 14/496,923, filed on Sep. 25,2014—now U.S. Pat. No. 9,036,609. Said application was a continuation ofapplication Ser. No. 13/304,852, filed Nov. 28, 2011, which claimspriority to U.S. Provisional Application No. 61/426,628, filed Dec. 23,2010 and is a Continuation-in-Part of application Ser. No. 12/251,187,filed Oct. 14, 2008 (now U.S. Pat. No. 8,068,871), which claims thebenefit of U.S. Provisional Application No. 61/016,062 filed, Dec. 21,2007. All applications hereby incorporated in their entireties herein byreference.

BACKGROUND

Embodiments of the invention are directed, in general, to communicationsystems and, more specifically, methods of reducing mediumcontamination.

Next-generation mobile devices will be able to access a variety ofnetwork technologies including, for example, worldwide interoperabilityfor microwave access (WiMAX) networks, wireless local area network(WLAN) networks, long term evolution (LTE) mobile telephony networks,personal area networks (PANs), wireless universal serial bus (USB)networks or BLUETOOTH® (BT) technology networks, etc. The variousapplications have different transmission timing requirements in order toprovide a needed quality of service (QoS). Quality of service refers tomechanisms for controlling resource reservation rather than the achievedservice quality. QoS is the ability to provide different priority todifferent applications, users, or data flows, or to guarantee a certainlevel of performance to a data flow, e.g., guarantee a required bitrate, delay, jitter, packet dropping probably, bit error rate, etc.Quality of service guarantees are important, for example, if the networkcapacity is insufficient or limited, especially for real-time streamingmultimedia applications such as voice over IP, online games and IP-TV,since these delay sensitive applications often require fixed bit rate.

The IEEE802.11 specification provides a quality of service controlprotocol that enables a service differentiation to be provided forpackets. For example, voice and e-mail traffic require different qualityof service levels to provide acceptable service quality. In particular,voice packets need to be delivered within strict delay bounds wherease-mail packets are more delay tolerant.

While increased access to these technologies will benefit users andoperators alike, interference among different technologies, particularlyonboard a single device, introduces difficulties during concurrentoperation of these technologies. For example, and as illustrated in FIG.1, wireless local area network (“WLAN”; 2.4-2.5 GHz) and othertechnologies, such as Bluetooth (“BT”; 2.4-2.4835 GHz) and WorldwideInteroperability for Microwave Access (“WiMAX”; 2.3-2.4 GHz and 2.5-2.7GHz), operate at relatively close and, in some cases, overlappingfrequency bands with respect to each other—so close, in fact, that theout-of-band emission by either technology may saturate the receiver ofthe other technology resulting in potential blocking. Therefore, theinterference between these two technologies operating in the same devicecreates challenges on the coexistence of the corresponding wirelessinterfaces of that device.

To solve the coexistence problem, in which WLAN technology is one of thesubsystems operating in the same device, time multiplexed operation havebeen proposed if both subsystems share the same antenna. For example, inthe case of WLAN and BT coexistence, BT voice calls take priority overother traffic flows in WLAN. During the time periods that the deviceoperates in BT mode, the WLAN operates in unscheduled automatic powersaving delivery (U-APSD) mode. During the time that the device operatesin WLAN mode, it sends a trigger frame (or a PS-Poll) to the APindicating that it is ready to receive packets. To protect the networkfrom the avalanche effect (caused by rate fallback mechanism due to thefact that the STA operating in BT can not send ACK packets to the AP,hence the AP reduces the transmission rate) the use of CTS-to-self hasbeen proposed as a viable solution. Thus, before the STA transits to theBT mode, it sends the CTS-to-self frame and reserves the medium untilthe time that BT transmission ends and the gap/idle BT interval starts.If both subsystems share the same antenna as well as a low noiseamplifier (LNA); then reception of packets in both subsystems ispossible. Transmission however, is not allowed. Even though thesubsystems can both receive, CTS2Self frame is sent to protect from theavalanche effect.

What is needed is a reduced NAV setting by CTS2Self frames by estimatingpacket received and data rate used to improved time optimization forsending of CTS2Self frames when receive/receive option is enabled forWLAN/BT subsystems.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is illustrative of different technologies and their operatingbands.

FIG. 2 illustrates an example wireless local area network (WLAN) with anaccess point and a plurality of wireless devices/stations, according toembodiments;

FIG. 3 illustrates an exemplary access point and/or wireless device,according to embodiments;

FIG. 4 illustrates an exemplary device, according to embodiments;

FIG. 5 illustrates an exemplary timing diagram comparing times forsending silencing frames;

FIG. 6 is a flowchart illustrative of an exemplary method ofcommunicating, according to embodiments;

FIG. 7 is a flowchart illustrative of an exemplary method of determininga preferred silencing frame transmission time, according to embodiments;

FIG. 8 is a flowchart illustrative of another exemplary method ofdetermining a preferred silencing frame transmission time, according toembodiments

FIG. 9 illustrates of NAV setting in accordance with an embodiment ofthe invention; and

FIG. 10 is a flowchart illustrative of an exemplary method ofcommunication, according to further embodiments of the invention.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, computer companies may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In the following discussion and inthe claims, the terms “including” and “comprising” are used in anopen-ended fashion, and thus should be interpreted to mean “including,but not limited to . . . .” Also, the term “couple” or “couples” isintended to mean either an indirect or direct electrical connection.Thus, if a first device couples to a second device, that connection maybe through a direct electrical connection, or through an indirectelectrical connection via other devices and connections. The term“system” refers to a collection of two or more hardware and/or softwarecomponents, and may be used to refer to an electronic device or devicesor a sub-system thereof. Further, the term “software” includes anyexecutable code capable of running on a processor, regardless of themedia used to store the software. Thus, code stored in non-volatilememory, and sometimes referred to as “embedded firmware,” is includedwithin the definition of software.

DETAILED DESCRIPTION

The invention now will be described more fully hereinafter withreference to the accompanying drawings. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Oneskilled in the art may be able to use the various embodiments of theinvention.

It should be understood at the outset that although exemplaryimplementations of embodiments of the disclosure are illustrated below,embodiments may be implemented using any number of techniques, whethercurrently known or in existence. This disclosure should in no way belimited to the exemplary implementations, drawings, and techniquesillustrated below, including the exemplary design and implementationillustrated and described herein, but may be modified within the scopeof the appended claims along with their full scope of equivalents.

In working toward solving the coexistence problem, especially when WLANtechnology is one of a plurality of network technology subsystemsoperating in a same device (i.e., onboard network technologysubsystems), time-multiplexed operation among the onboard networktechnology subsystems is useful. For example, and not by way oflimitation, in the case of WLAN and BT coexistence, BT voice calls mayhave priority over other traffic flows in a WLAN. As part oftime-multiplexed operation in such exemplary device, during the timeperiods that the device operates in active BT mode, the WLAN services onthe same device preferably operate in unscheduled automatic power savingdelivery (U-APSD) mode. When the device switches to operate in activeWLAN mode, the device sends a trigger frame (or a PS-Poll) to the accesspoint (AP) indicating that the device is ready to act as a receiver,e.g., to receive packets of information. The AP may also be referred toherein as a transmitter, e.g., a transmitter of data packets. For thesake of discussion at this point, assume the transmitted packets ofinformation—normally containing data—are correctly routed to the deviceas the intended recipient. Transmission becomes problematic if thepackets addressed to the device are sent by the AP within the timeperiod that the device is operating in active WLAN mode but the devicehas insufficient time to reply with an ACK (in case of immediateacknowledgment) because, for example, the device has switched back toactive BT mode (e.g., incoming voice data) and misses the packettransmitted by the AP; as a result, no ACK would be sent by the device.As a further example, if the packets sent by the AP are not sent withinthe time interval that the device is operating in active WLAN mode,again no ACK would be sent by the device.

When the AP fails to receive an ACK from its intended recipient device,a transmission rate-fall back mechanism commences at the AP. Thismechanism reduces the transmission rate used to send subsequent packetsfrom the AP to the device based on the failure to receive an ACK fromthe STA. In other words, when the AP transmits a packet to the intendeddevice—also referred to herein as a STAtion (STA or STA)—and the APreceives no corresponding ACK from that device/STA, then the AP reducesthe current transmission rate to a lower (slower) transmission ratebecause the AP assumes the communication channel between itself and theintended STA is bad.

Although the packet size does not change, as the transmission ratedecreases, the total duration of the packet lengthens, which in turnresults in an increased probability that the duration of the AP wirelesstransmission and the time the device is involved with a BT receptionwill time-wise overlap. Worse, as the packets transmitted over thechannel medium occupy ever-lengthening intervals, the correspondingprobability of a collision (time-wise overlapping) with the use by thedevice/STA of the medium on behalf of a different network technologysubsystem (in the present example, in active BT mode), quicklyincreases. With the increased probability of collisions comes increasedlikelihood of the AP more often failing to receive an ACK, and inresponse continuing to lower the transmission rate (thereby increasingthe duration of the transmission of the packet and, naturally,increasing the probability of a further collision such that the STAfails (again) to receive the packet, and fails (again) to send an ACK.It can be quickly appreciated that as this cycle proceeds, performanceof the device STA rapidly deteriorates. This is unacceptable for manyreasons, including violation of QoS (quality of service) requirements.Another reason stems from the practice of an AP to continue reducing thetransmission rate until reaching a predetermined threshold, at whichtime the AP may unilaterally disconnect the device/STA from the networkbecause the AP would not be able to transfer much if anything at all tothe device above that threshold. The rapid deterioration inperformance—and associated increase in probability of collision—is whatwill be referred to herein as an “avalanche effect” because, as timeprogresses, the message becomes buried and unrecoverable/lost. Simply,the avalanche effect reflects the phenomenon that the probability oflosing a packet, and risk of potentially being unwillingly disconnectedfrom the system, increases as the rate of transmission decreases.

To protect the network from the avalanche effect, embodiments employ asilencing frame. One example of a silencing frame, and not by way oflimitation, would be a clear-to-send-to-self (CTS-to-self) frame. Thus,before the STA transitions to an active BT mode, the STA device sendsthe silencing frame and reserves the medium until the time correspondingto the end of the active BT mode or the end of that BT transmissionends—as the case may be—and the next lower priority network technology,e.g., WLAN, interval commences. However, it has become apparent that theuse of silencing frames to protect priority interval transmissions fromthe avalanche effect in coexisting dissimilar technology subsystemnetworks drastically reduces the throughput of lower priority interval(e.g., WLAN, etc.) transmissions because devices/stations must defer (besilent) during the time set by the duration field (NAV) in the silencingframe. Thus, sending the silencing frame too early, results in otherSTAs/devices in the network—for example those on the WLAN—having to bequiet (deferring) for at least the entire BT active mode interval. Thisearly deference, in turn, results in significantly decreased throughputof the network.

In light of the foregoing, embodiments are directed in general, tocommunication systems, and more specifically, to systems and methods ofsilencing wireless devices in coexistence networks to avoid triggeringthe AP transmission rate fall-back mechanism and still improve theperformance of network resources. Embodiments provide systems andmethods to optimize the time when to send silencing frames, and hence,improve the overall network throughput while avoiding avalanche effects.

FIG. 2 illustrates an example wireless local area network (WLAN) 200with a plurality of wireless devices/stations—referred to individuallyherein as device, station, STA or device/station—and an access point(AP), according to embodiments. It should be appreciated that thenetwork of FIG. 2 is meant to be illustrative and not meant to beexhaustive; for example, it should be appreciated that more, differentor fewer communication systems, devices and/or paths may be used toimplement embodiments. To provide wireless data and/or communicationservices (e.g., telephone services, Internet services, data services,messaging services, instant messaging services, electronic mail (email)services, chat services, video services, audio services, gamingservices, etc.), the exemplary WLAN 200 comprises access point (AP) 220and any of a variety of fixed-location and/or mobile wireless devices orstations (STAs), four of which are respectively designated in FIG. 2with reference numerals 210A, 210B, 210C and 210D. Exemplary devices 210include any variety of personal computer (PC) 210A with wirelesscommunication capabilities, a personal digital assistant (PDA) 210B, anMP3 player, a wireless telephone 210C (e.g., a cellular phone, a Voiceover Internet Protocol (VoIP) telephonic functionality, a smart phone,etc.), and a laptop computer 210D with wireless communicationcapabilities, etc. At least one of AP 220 and STAs 210A-D are preferablyimplemented in accordance with at least one wired and/or wirelesscommunication standard (e.g., from the IEEE 802.11 family of standards).Further, at least one device 210 comprises a plurality of co-existingwireless network technology subsystems onboard the at least one device210. In at least some embodiments, device 210 consists of a WLAN networkand a BT network. The WLAN network may handle File Transfer Protocol(FTP), with internet file download, and e-mail traffic, while the BTnetwork may handle synchronous connection-oriented high-quality voicelevel 3 (SCO HV3) traffic. STA is a WLAN and BT node and transmissionsin different networks are preferably achieved via a time-duplexingapproach (ON/OFF). It will be noted that reference to “STA” (station)may be used herein as a shorthand reference to “STA1”, “device 210” and“device 410” during respective discussions to aid in ease ofunderstanding.

In the example of FIG. 2, to enable the plurality of devices/STAs 210A-Dto communicate with devices and/or servers located outside WLAN 200, AP220 is communicatively coupled via any of a variety of communicationpaths 230 to, for example, any of a variety of servers 240 associatedwith public and/or private network(s) such as the Internet 250. Server240 may be used to provide, receive and/or deliver, for example, anyvariety of data, video, audio, telephone, gaming, Internet, messaging,electronic mail, etc. service. Additionally or alternatively, WLAN 200may be communicatively coupled to any of a variety of public, privateand/or enterprise communication network(s), computer(s), workstation(s)and/or server(s) to provide any of a variety of voice service(s), dataservice(s) and/or communication service(s).

The systems and methods described herein may be implemented on anygeneral-purpose computer with sufficient processing power, memoryresources, and network throughput capability to handle the necessaryworkload placed upon it. FIG. 3 illustrates an exemplary,general-purpose computer system suitable for implementing at least oneembodiment of a system to respond to signals as disclosed herein.Illustrated exemplary device 300 which may be an access point and/orwireless device, according to embodiments. It should be expresslyunderstood that any device on, for example, WLAN 200 or otherembodiments, may at times be an access point and at other times be astation. It should also be understood that in some embodiments, theremay be at least one dedicated access point, with any number of devicesacting as stations.

Exemplary device 300 comprises at least one of any of a variety of radiofrequency (RF) antennas 305 and any of a variety of wireless modems 310that support wireless signals, wireless protocols and/or wirelesscommunications (e.g., according to IEEE 802.11n). RF antenna 305 andwireless modem 310 are able to receive, demodulate and decode WLANsignals transmitted to and/or within a wireless network. Likewise,wireless modem 310 and RF antenna 305 are able to encode, modulate andtransmit wireless signals from device 300 to and/or within a wirelessnetwork. Thus, RF antenna 305 and wireless modem 310 collectivelyimplement the “physical layer” (PHY) for device 300. It should beappreciated that device 300 is communicatively coupled to at least oneother device and/or network (e.g., a local area network (LAN), theInternet 250, etc.). It should further be understood that illustratedantenna 305 represents one or more antennas, while the illustratedwireless modem 310 represents one or more wireless modems.

The exemplary device 300 further comprises processor(s) 320. It shouldbe appreciated that processor 320 may be at least one of a variety ofprocessors such as, for example, a microprocessor, a microcontroller, acentral processor unit (CPU), a main processing unit (MPU), a digitalsignal processor (DSP), an advanced reduced instruction set computing(RISC) machine (ARM) processor, etc. Processor 320 executes codedinstructions 355 which may be present in a main memory of the processor320 (e.g., within a random-access memory (RAM) 350) and/or within anon-board memory of the processor 320. Processor 320 communicates withmemory (including RAM 350 and read-only memory (ROM) 360) via bus 345.RAM 350 may be implemented by DRAM, SDRAM, and/or any other type of RAMdevice; ROM 360 may be implemented by flash memory and/or any other typeof memory device.

Processor 320 implements MAC 330 using one or more of any of a varietyof software, firmware, processing thread(s) and/or subroutine(s). MAC330 provides medium access controller (MAC) functionality and furtherimplements, executes and/or carries out functionality to facilitate,direct and/or cooperate in avoiding avalanche effect. MAC 330 isimplemented by executing one or more of a variety of software, firmware,processing thread(s) and/or subroutine(s) with the example processor320; further, MAC 330 may be, additionally or alternatively, implementedby hardware, software, firmware or a combination thereof, includingusing an application specific integrated circuit (ASIC), a programmablelogic device (PLD), a field programmable logic device (FPLD), discretelogic, etc.

Device 300 also preferably comprises at least one input device 380(e.g., keyboard, touchpad, buttons, keypad, switches, dials, mouse,track-ball, voice recognizer, card reader, paper tape reader, etc.) andat least one output device 385 (e.g., liquid crystal display (LCD),printer, video monitor, touch screen display, a light-emitting diode(LED), etc.)—each of which are communicatively connected to interface370.

Interface 370, additionally or alternatively, communicatively coupleswireless modem 310 with processor 320 and/or MAC 330. Interface 370enables interface to, for example and not by way of limitation, Ethernetcards, universal serial bus (USB), token ring cards, fiber distributeddata interface (FDDI) cards, network interface cards, wireless localarea network (WLAN) cards, etc. to enable device 300 to communicate withother devices and/or communicate via Internet 250 or at least oneintranet. With such a network connection, it is contemplated thatprocessor(s) 320 would be able to receive information from at least onetype of network technology, and/or output information to at least onetype of network technology in the course of performing theherein-described processes. It should be appreciated that interface 370implements at least one of a variety of interfaces, such as an externalmemory interface, serial port, communication internal to device 300,general purpose input/output, etc.

Device 300 further comprises at least two dissimilar network technologysubsystems 340; as a result, device 300 is said to have co-existingnetwork technology. “Dissimilar” is used in this context to mean that atleast one of the subsystems 340 is from a different network technologythan another one of the subsystems 340. It should be understood thatsome embodiments of subsystems 340 may have their own dedicated wirelessmodem and antenna, while other embodiments may share either or both of awireless modem and antenna. Embodiments of device 300 comprise at leasttwo wireless network technology subsystems 340. FIG. 3 illustratesnetwork technology subsystems 340 _(A)-340 _(N), where N=the numbernetwork technology subsystems in device 300. Examples of networktechnologies that may be represented by such subsystems include, but arenot limited to, worldwide interoperability for microwave access (WiMAX)networks, wireless local area network (WLAN) networks, long termevolution (LTE) mobile telephony networks, personal area networks(PANs), wireless universal serial bus (USB) networks, BLUETOOTH (BT)networks, etc. Processor 320 interacts with network technologysubsystems 340 via corresponding interfaces 470 _(A)-470 _(N) (see FIG.4) implemented by interface 370. It should be appreciated that, for theease of illustration, only two or three such network technologies may bediscussed in connection with any particular embodiment, that more orfewer such technologies may be onboard a device, and that the presentteachings apply equally thereto.

Before proceeding further, it should be understood that, for ease ofunderstanding, embodiments will mostly be described herein in connectionwith a single lower priority technology network and a single higherpriority technology network. However, embodiments should in no way beconsidered limited to just these two onboard technology networksubsystems. In some embodiments, there may be additional and/ordifferent onboard technology network subsystems. In some embodiments,there may be at least one lower priority technology network (e.g., WLAN,etc.) and a plurality of higher priority technology networks (e.g., BT,WiMAX, etc.). It should be appreciated that the scope of the presentinvention is not intended to be constrained to a single lower prioritytechnology network and a single higher priority technology networkonboard a device.

As illustrated in FIG. 4, an exemplary device 410 comprises a controller420 and interfaces 470 _(A)-470 _(N), where N=the number of onboardnetwork technologies corresponding to each of the respective dedicatedinterfaces. Controller 420, in turn, comprises monitor 430, calculator440, timer 450 and scheduler 460. It should be appreciated that althoughthe example device of FIG. 4 illustrates controller 420 as comprising,monitor 430, calculator 440, timer 450 and scheduler 460, that some orseveral of these elements may be external to controller 420. Moreover,it should also be appreciated that, in many embodiments, controller 420also comprises additional functionality such as security inputs (oftenfrom a user), managing power saving features for the interfaces, etc.Embodiments of device 410 consist of wireless—and, in some cases,wired—links. Because at least some of the links are wireless, somecommunications may interfere with each other. For example, it may not bepossible for two links to be active at the same time because thetransmission of one interferes with the transmission of the other.Preferably time-division multiplexing is used where interfering linksoperate at different times, but embodiments of scheduler 460 preferablyunderstand the priority and parameters of each onboard networktechnology, as well as any negotiated parameters established duringinitial association with an AP.

Controller 420 schedules the duration each active network traffic flowmay keep priority on device 410's resources. There are a variety ofscheduling options, one of which may be fair allocation. Generally, thedevice alternates among the various active traffic flows—correspondingto each of the initiated network technology subsystems represented ondevice 410—depending upon each service/traffic flow's priority asdetermined by scheduler 460. Each network preferably takes sequentialturns in using device 410's resources to send packets to—or otherwisecommunicate with—networks outside of device 410. Often, the schedulerwill establish a periodic transmission time for each onboard technologynetwork subsystem, for improved and efficient use of device 410'sresources. The periodic transmission(s) may also be provided to theAP(s) within any particular network to enable network-specifictransmissions by the AP(s) during known network-specific active modes(reception) intervals. Scheduler 460 knows to transmit silencing frameduring the period of Δt until start of higher priority active modeinterval—if it can—otherwise, no silencing frame is to be transmitted.Once the higher priority active mode interval has ended, and a lowerpriority active mode has begun, scheduler 460 will again attempt totransmit a silencing frame during the period of Δt—as determined bycalculator 440—until start of higher priority active mode interval. Asbefore, if the silencing frame cannot be transmitted prior to the startof the next immediate interval for higher priority active mode, nofurther effort is made to transmit a silencing frame. This processrepeats so long as higher priority active mode intervals continue to bescheduled.

Controller 420 calls monitor 430 to monitor traffic flow; in someembodiments, monitor 430 only monitors the existence of active trafficflows onboard device 410, while in other embodiments, monitor 430 alsomonitors what network technology (e.g., WLAN, BT, WiMAX, etc.) and whattype of transmission (e-mail, streaming video, VoIP, etc.) are affected.It should be appreciated that embodiments involve traffic flowsregardless of type of traffic or whether the traffic is unicast,broadcast, multicast, etc.

Additionally, in at least some embodiments, controller 420 employsmonitor 430 to track changes in the active traffic flows. If monitor 430determines that there has been a change in at least one of the activetraffic flows, it also identifies the change. As one example, and not byway of limitation, a WLAN MAC sends a trigger to controller 420indicating that it wants to add traffic, i.e., initiate a traffic flow.Embodiments of scheduler 460 dynamically focus on scheduling andprioritizing among the service calls (requests) based on the informationgathered by monitor 430.

Embodiments of calculator 440 perform various calculating functions,including, but not necessarily limited to, determining Δt to be used byscheduler 460. Calculator 440 employs timer 450, as well as registers,to establish the transit time(s) between AP and STA (device 410 in theFIG. 4). At least some embodiments of calculator 440 calculate the Δttime interval as follows:Δt=max_i(AP_to_STA1_Tx_Time+STA1_to_AP_Tx_Time)where “i” is the traffic flow indication from the AP to the STA and thelatest duration values for each traffic flow duration are used to selectthe maximum value.

It should be appreciated that the time taken to transmit the silencingframe (e.g., CTS-to-self frame, in the present example) and, in someembodiments, trigger frame (e.g., trigger frame-ACK, in the presentexample) from STA to the AP can be calculated because the STA device isthe one initiating the transmission. Moreover, the time that the APtakes to transmit to the STA device can also be estimated from earliertransmissions, or may be a negotiated maximum transmitted size from theAP to STA in view of their negotiated data rates upon initialassociation. It should be appreciated that if the time the AP takes totransmit to the STA device is estimated from previous transmissions, itis preferred that the data rate and packet size from the most recentreceived transmission should be selected as the parameters from which todetermine the AP to STA transmission time. Moreover, if there aremultiple active traffic flows from AP to STA (e.g., belonging todifferent categories that may have different data rates and differentpacket sizes), because the STA will not know what the AP will send inresponse to the STA device's silencing frame, at least some embodimentsof STA device preferably choose the maximum transmission time (datarate×packet size) among the transmission times most recently receivedwith respect to each of the multiple active traffic flows. It should beappreciated that in some embodiments, the maximum duration among theearlier transmissions could be selected, although this selection tendsto minimize the benefits of the present invention. In at least someembodiments, the time to transmit the silencing frame (plus triggerframe, depending upon embodiments) plus time the AP takes to transmit tothe STA equals Δt. It should be appreciated that once eitherparameter—data rate and/or data packet size—has been calculated, it maybe stored in memory or a hardware register to be used in futuredeterminations of preferred time for transmission of a silencing frame,including use for comparisons among respective parameter values toascertain quality of medium, etc.

Calculator 440 adds the established transit time(s), i.e., Δt, to theduration of the at least one higher priority interval to be protected todetermine a duration (value). In some embodiments, calculator 440 alsosubtracts the determined duration from the known ending time of the atleast one higher priority interval to be protected and identifies theresulting time as the preferred time for transmission of a silencingframe; this preferred time is provided to scheduler 460. In otherembodiments, calculator 440 subtracts Δt from the known beginning timeof the next immediate at least one higher priority interval to beprotected and identifies the resulting time as the preferred time fortransmission of a silencing frame; as with other embodiments, thispreferred time is provided to scheduler 460. Scheduler 460 directscontroller 420 to transmit a silencing frame (e.g., CTS2S frame) at thepreferred time. The preferred time occurs Δt prior to the beginning edgeof BT active mode (FIG. 5). It should be appreciated that “Δt” will beused to refer to the amount of time (a value) prior to the nextimmediate higher priority technology network active mode interval duringwhich it is preferred for the device to transmit a silencing frame. Asnoted above, if controller 420 (via scheduler 460) is unable to transmita silencing frame during the Δt period of time, then no silencing frameis sent with respect to the next immediate higher priority active modeinterval.

Calculator 440 also determines the end time of the predeterminedtransmission window by subtracting the time it takes to at leastcompletely transmit the silencing frame from the known beginning time ofthe next immediate at least one higher priority interval to beprotected; calculator 440 identifies the resulting time as the endingtime of the predetermined transmission window. By so determining theending time of the transmission window, the scheduler 460 directscontroller 420 to complete the transmission of the silencing frame insufficient time prior to the beginning of the interval(s) to beprotected—assuming the medium is not busy. If the medium is busy so thatthe transmission of the silencing frame cannot be completed prior to thebeginning of the interval(s) to be protected (i.e., within the beginningand ending times of the predetermined transmission window), thenscheduler 460 directs controller 420 to send no silencing frame, anddevice/STA 410 transitions to the first of the next immediate at leastone higher priority active modes.

It should also be appreciated that a silencing frame cannot betransmitted if the medium is busy (and that if the medium is not busy,the frame is transmitted). However, if the medium is busy, STA will waituntil the medium becomes idle again before attempting to transmit thesilencing frame. If the medium does not become idle again before thebeginning of the next immediate higher priority active mode interval,controller 420 will not send a silencing frame.

On the other hand, if the silencing frame can be transmitted before thestart of higher priority (e.g., BT) activity interval, i.e., sometimeduring the Δt period of time, then the network allocation vector (NAV)or duration is shortened to accommodate the remaining duration of Δttransmission window plus the duration of the at least one higherpriority technology network active mode interval (e.g., ending ofinterval entitled “BT ON” in interval 520 or ending of interval entitled“WiMAX ON” in interval 530, both of FIG. 5). In other words, the valueof NAV set at the beginning of Δt transmission window as calculated bycalculator 440 is correspondingly reduced by the amount of time themedium remains busy after the maximum preferred frame transmission timehas passed.

During certain intervals, a STA device participates in lower prioritytechnology (WLAN) network, while during other intervals, it participatesin higher priority technology networks (BT and WiMAX). In order to avoidthe avalanche effect, a silencing frame (e.g., a CTS-to-self frame) istransmitted to the AP (from STA). If the silencing frame transmitted isa clear-to-send-to-self frame, it is preferably followed by a triggerframe (which could be a PS-Poll or a quality of service (QoS) Nul frame)indicating to the AP that STA is ready to receive data packets. Thesilencing frame—in this example, a CTS-to-self frame and subsequentconsecutive trigger frame—have the network allocation vector (NAV) setto protect any higher priority technology network (in these examples, BT(interval 520) or BT and WiMAX (interval 530)) active mode period. Thus,the NAV is set to decrement until reaching the zero value at the endingof the higher priority active mode operation duration (which durationmay encompass the total duration of more than one higher prioritytechnologies' active modes). All other devices on the particularcorresponding technology network, in this example WLAN, defer whiletheir respective NAVs also decrement. Once a deferring device's NAVdecrements to zero, the device no longer defers from accessing themedium, or sensing the medium to determine whether the medium isavailable. Hence, during the time identified in the transmittedsilencing frame, no other—in this example—WLAN STA can transmit orreceive from the AP. However, as noted above, the time at which asilencing frame is sent impacts the WLAN performance. To improve WLANthroughput, it is preferred that the silencing frame is not sent until·t time interval before the start of the next immediate higher priority(e.g., BT, WiMAX, etc.) period.

It should be appreciated that what is being referred to herein as asilencing frame may, in some embodiments, comprise more than onetransmitted frame, e.g., such as a Clear-to-Send-to-Self frameimmediately followed with a trigger frame. In such embodiments, thetrigger frame is sent to prevent the other devices on the particularnetwork from assuming that the original Clear-to-Send message wasunsuccessful and begin to try to access the medium. However, once thetrigger frame follows the Clear-to-Send frame, the other devices on theparticular network set their respective NAV to the duration specified inthe Clear-to-Send-to-Self frame, and defer until their respective NAVdecrements to zero before again attempting to access the medium.

Furthermore, at least some embodiments enable transmission of asilencing frame from STA to take precedence by enabling STA to transmita silencing frame after point coordination function interframe spacing(PIFS) time interval that the medium is idle. Thus, instead of waitingthe customary distributed inter frame space (DIFS) interval beforetrying to gain access to the medium, it is preferred that the STA waitsa PIFS interval before trying to gain access to the medium.

FIG. 5 illustrates an exemplary timing diagram of the operation of anembodiment of STA. In each of exemplary intervals 510, 520 and 530, theSTA device completes at least one higher priority network active modeand at least one lower priority network active mode. The timing diagramillustrates the timing of transmission of three silencing frames, underthree different scenarios. In interval 510, the silencing frame israndomly transmitted prior to the start of the high priority active modeoperation interval; however, in intervals 520 and 530, the silencingframe is transmitted according to embodiments. Specifically, the firstframe is sent, without benefit of present embodiments, during interval510 by STA at a random time at any time during the lower priority activemode interval (WLAN ON, in this example); the second frame is sent, withthe benefit of at least one present embodiment, during interval 520 bySTA at a preferred time; and the third frame is sent, with benefit of atleast one present embodiment, during interval 530 by STA at a respectivepreferred time. Each preferred time is determined by at least someembodiments as described above. FIG. 5 corresponds to a device STA thatalternates among at least two dissimilar network technologies. As notedabove, it should be understood that embodiments of the device may switchamong more than two dissimilar network technologies. Specifically, thereare three exemplary intervals (510, 520, 530) illustrated—eachcomprising at least one higher priority active mode interval (BT activemode ON and/or WiMAX active mode ON) and one lower priority active modeinterval (WLAN active mode ON). In intervals 510 and 520, STA reservesthe medium until the end of the BT active mode (ending of intervalentitled “BT ON” in FIG. 5) in exemplary interval 520. It should befurther understood that although the silencing frame of transmissions540, 550 and 560 are illustrated to be “CTS2S tx” (clear-to-send-to-selftransmission), that other types of silencing frames may be used instead.

Within exemplary interval 510, STA device transmits a silencing frame540 with duration information for all interested devices to set theirNAVs equal to the value of NAV_(A). It can be seen that there is no Δtin the interval bounded by NAV_(A). It should be understood that thetransmission 540 of a silencing frame occurs randomly at any time withinthe lower priority technology active mode (e.g., “WLAN ON” in thepresent example). The time to transmit silencing frame is notpredetermined or calculated to be at a specific time. Once it is sent,all interested devices on the respective network set their NAVs to thevalue corresponding to NAV_(A). Because the timing of transmission 540is random at any time within the lower priority technology active mode,transmission 540 regularly—and unnecessarily—ties up network resourceswhich are obliged to defer until their respective NAVs have completelydecremented.

Within exemplary interval 520, STA device transmits a silencing frame550 with duration information for all interested devices to set theirNAVs equal to the value of NAV_(B). However, according to embodiments,the silencing frame may only be sent by the STA during the predeterminedtransmission window identified in interval 520 by “Δt”. As noted above,Δt transmission window is determined to preferably minimize the amountof time the STA device ties up corresponding technology networkresources. The transmission 550 of silencing frame may occur at any timeduring the predetermined Δt transmission window, depending upon whetherthe medium is busy, and in some embodiments, whether the STA waits PIFSinstead of DIFS after the medium becomes available to transmit. If themedium is not busy, it is preferred that the STA transmit the silencingframe as close to the beginning of the predetermined Δt transmissionwindow as possible. If STA cannot transmit the silencing frame duringthe Δt transmission window, it will not transmit a silencing frame atall to protect the upcoming higher priority technology active mode(e.g., “BT ON”, in the present illustration).

Within exemplary interval 530, STA device transmits a silencing frame560 with duration information for all interested devices to set theirNAVs equal to the value of NAV_(C). However, according to embodiments,the silencing frame may only be sent by the STA during the transmissionwindow identified in interval 530 by “Δt”. As with the embodiment ofinterval 520, Δt transmission window of interval 530 is determined topreferably minimize the amount of time the STA device ties upcorresponding technology network resources. The transmission 560 ofsilencing frame may occur at any time during the Δt transmission window,depending upon whether the medium is busy, and in some embodiments,whether the STA waits PIFS instead of DIFS after the medium becomesavailable to transmit. If the medium is not busy, it is preferred thatthe STA transmit the silencing frame as close to the beginning of thepredetermined Δt transmission window as possible. If STA cannot transmitthe silencing frame during the Δt transmission window, it will nottransmit a silencing frame at all to protect the at least one upcominghigher priority technology active mode(s) (e.g., “BT ON” and “WiMAX ON”,in the present illustration).

It should be noticed that the Δt transmission window ends prior to thebeginning of the next immediate string of at least one higher prioritytechnology network active modes in intervals 520 (“BT ON”) and 530 (“BTON and WiMAX ON”), respectively. The silencing frame transmission gap570 shown in each interval (520,530) illustrates the time it takes tocomplete transmission of the silencing frame. In some embodiments, gap570 also includes time for response from another device on the networkand/or the time required for the device to switch from one network tothe other. It is preferred that the transmission of the silencing framestart during the Δt transmission window. It is further preferred that ifthe transmission of the silencing frame is started just prior to the endof the Δt transmission window, the transmission of the silencing framewill be completed prior to the commencement of the next immediate(imminent) string of at least one higher priority active modes.

In exemplary interval 530, however, STA reserves the medium until theend of the WiMAX active mode (ending of interval entitled “WiMAX ON” inFIG. 5). Thus, STA device sends a CTS-to-self frame (example of asilencing frame) to protect all consecutive higher priority frames inthe next immediate string of higher priority frames. In exemplaryinterval 530, STA device sends a silencing frame to protect thetransmission from STA to AP, the acknowledgement from the AP to STA, theBT ON (active mode interval) and the WiMAX ON (active mode interval). Itshould also be understood that additional higher priority technologynetworks may immediately follow the two illustrated in FIG. 5; in suchembodiments, STA would send a silencing frame at a preferred time whichwill protect all such consecutive high priority network activity (activemode intervals). In other words, the duration field of the silencingframe will be set to protect a string of as many consecutive higherpriority active modes as needed for a device.

FIG. 6 illustrates a method for communicating. At block 610, thecontroller monitors traffic flow. Traffic flow monitored may compriseactivity on the medium, as well as coordination of a device's shiftbetween higher and lower priority active modes—for example, and not byway of limitation, either on a predetermined alternation schedule orbased on a detected incoming transmission addressed to the device.Controller calculates the duration, as well as timing, of a silencingframe transmission time window (block 620) and transmits a silencingframe only during the calculated window (block 630). In someembodiments, if the silencing frame was a clear-to-send-to-self frame,the device may immediately follow with a transmission of a triggerframe. Because the functionality of block 640 is optional—for example,it might not be used if the silencing frame transmitted by the device isnot a clear-to-send-to-self frame—block 640 is shown in dashed outline.

FIG. 7 illustrates an exemplary method of calculating a silencing frametransmission time window (block 620 of FIG. 6), according toembodiments. It should be understood that although block 620 of FIG. 7is shown as comprising functional blocks 710, 720 and 730, block 620 maycomprise additional function blocks, or further combine thoseillustrated as desired. It should also be appreciated that any of thefunctional blocks 710, 720 and 730 may instead comprise a differentelement of a device.

At block 710, the transmission times from STA to AP and from AP to STAare determined. The transmission time from STA to AP can be determinedbecause the transmission is from the STA. In some embodiments, thetransmission times from the AP to STA are additionally or alternatively,measured and subsequently stored. The latest data rate and packet sizeare preferably selected to determine the transmission time from the APto STA. The determined transmission times from AP to STA and STA to APare added together (block 720) to determine the value of Δt, which isthe duration of the silencing frame transmission time window. This valueis subtracted (block 730) from the start time of the next immediatehigher-priority technology subsystem network active mode to identify theΔt transmission window, which window bounds the time for STA to transmita silencing frame to avoid avalanche effect while increasing networkthroughput. In some embodiments, the value of Δt is subtracted from thestart time of an immediately following string of consecutivehigher-priority technology subsystem network active modes. In someembodiments, the value may be calculated and stored in advance, thenretrieved when the next immediate lower priority active mode begins. Itshould be appreciated that it is intended that “string” as used hereinshall mean one or more.

Returning to block 630 of FIG. 6. STA may only transmit a silencingframe during the respective Δt transmission window to protect theupcoming at least one consecutive higher priority active modes. However,the STA device cannot transmit a silencing frame at all if the medium isbusy. Thus, when the medium is busy, embodiments of STA device mustdefer and wait until the medium is not busy before transmitting asilencing frame. Thus, the STA's NAV is set at the beginning of therespective Δt transmission window, and is decremented until the mediumis free. Upon accessing the medium, the value of then-decremented NAV isthen transmitted as part of the silencing frame and follow-on triggerframe, if any.

FIG. 8 illustrates another exemplary method of calculating a preferredsilencing frame transmission time (block 620 of FIG. 6), according toembodiments. It should be understood that although block 620 of FIG. 8is shown as comprising functional blocks 810, 820, 830 and 840, block620 may comprise additional function blocks, or further combine thoseillustrated as desired. It should also be appreciated that any of thefunctional blocks 810, 820, 830 and 840 may instead comprise a differentelement of a device.

At block 810, the transmission times from STA to AP and from AP to STAare determined. The transmission time from STA to AP can be determinedbecause the transmission is from the STA. In some embodiments, thetransmission times from the AP to STA are additionally or alternatively,measured and subsequently stored. The latest data rate and packet sizeare preferably selected to determine the transmission time from the APto STA. The determined transmission times from AP to STA and STA to APare added together (block 820) to determine the value of Δt, which isthe duration of the silencing frame transmission time window. This valueis added (block 830) to the total duration of the immediately upcomingstring of at least one consecutive higher priority active modes whichare to be protected. It should be appreciated that the duration when ahigher priority technology network is active (in active mode) may alsobe referred to herein as an interval. As an example, and not by way oflimitation, the total duration of the immediately upcoming at least onestring of consecutive higher priority active modes in interval 530 ofFIG. 5 would be the total combined duration of the BT ON and WiMAX ONperiods. Returning to FIG. 8, the resulting sum from block 830 issubtracted from the end time of the last higher priority active mode inthe next immediate higher-priority technology subsystem network activemode (block 840) to identify the beginning of the Δt transmissionwindow, which window bounds the time for STA to transmit a silencingframe to avoid avalanche effect while increasing network throughput. Insome embodiments, the value may be calculated and stored in advance,then retrieved when the next immediate lower priority active modebegins.

It should be appreciated that the total duration to be protected by thesilencing frame preferably consists of the sum of the duration remainingof the predetermined transmission time window interval after the time ittakes to transmit the silencing frame and the duration of theimmediately upcoming string of at least one consecutive higher priorityactive mode interval.

FIG. 9 is illustrative of NAV setting for RxRx 900. Next generationwireless networks will include different subsystems in the same device.A mechanism that further improves the performance of the network byoptimizing time reserved by CTS2Self frames being sent is disclosed.Hence, the overall throughput increases, while maintaining throughput atthe coexistence node.

FIG. 9 is illustrative of Bluetooth™ and WLAN systems. Blocks 901 showsfree blocks, 902 receive Rx and 905 transmission Tx in Bluetooth™. 907depicts not allowed blocks for WLAN. 933 depicts data transmission Txand WLAN Ack 935. Bluetooth™ BT is protected by CTS2Self NAV 920. Theduration of CTS2Self is 910.

Transmission of CTS2Self frames for shared antenna and shared LNA forboth subsystems is different with the case when the LNA is not shared.FIG. 9 is illustrative of what happens when reception window (i.e.receive-receive RxRx 900) is possible for both WLAN and BT. WLAN mayreceive during BT Rx if the data packet transmitted from the AP to thecoexistence node plus the short interframe spacing (SIFS) makes the WLANAck 935 to be transmitted after BT packet reception has ended. However,the time duration of the data packet transmitted from the AP depends onthe packet size, as well as on the physical rate at which the packet istransmitted. HencePck_duration_from_AP=f(packet_size_from_ap,ap_phy_rate).

Packet size statistics may be collected by observing the packetsarriving from the AP over a duration of time, while the ap_phy_rate maybe the last rate at which the packet from the AP was received at thecoexistence node. Hence, the NAV duration at the CTS2Self frame sentfrom the coexistence node may be:Nav_duration=RxT_time+BT_Slot_duration*2−(BT_Slot_duration−BT_pck_rx_duration)−Pck_duration_from_AP−sifs_time_duration

Calculation of RxT_time may follow the procedure explained above. Notethat an average backoff value may also be substracted from the aboveequation, where the backoff indicates that the AP (or other STAs) mayneed to perform a backoff procedure at the end of NAV set by CTS2Selfframe before a packet is transmitted. Further optimization may beobtained if the Pck_duration_from_AP is larger than BT_pck_rx_duration.In that scenario, the Nav_duration set by CTS2Self may cover minimum upto the end of BT packet duration for BT Tx.

FIG. 10 is a flowchart illustrative of an exemplary method of receivingtransmissions according to embodiments. It should be understood thatalthough block 1000 of FIG. 10 is shown as comprising functional blocks1010, 1020 and 1030, block 1000 may comprise additional function blocks,or further combine those illustrated as desired. It should also beappreciated that any of the functional blocks 1010, 1020 and 1030 mayinstead comprise a different element of a device.

At block 1010, a predetermined transmission window is calculated. Atleast two dissilmilar networks are transmitting at 1020. At block 1030,a receiver receives the two transmissions from each of the at least twodissimilar wireless network technology subsystems during thepredetermined reception window.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions,and the associated drawings. Therefore, the above discussion is meant tobe illustrative of the principles and various embodiments of thedisclosure; it is to be understood that the invention is not to belimited to the specific embodiments disclosed. Although specific termsare employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation. It is intended that thefollowing claims be interpreted to embrace all such variations andmodifications.

What is claimed is:
 1. A communications device, comprising: atransceiver comprising at least two dissimilar wireless networktechnology subsystems, at least one subsystem of which is lower prioritythan at least another of the dissimilar subsystems, the transceiver ableto calculate a transmission window to end by at least a duration of timeto complete transmission of the silencing frame prior to the beginningof next immediate string of at least one higher priority networktechnology subsystem interval, and transmit a silencing frame during alower priority technology network interval during the transmissionwindow.
 2. The communications device of claim 1, wherein thetransmission window is calculated determining by adding a plurality oftransmission times together to determine duration of the transmissionwindow.
 3. The communications device of claim 2, wherein the silencingframe is transmitted at beginning of the calculated transmission window.4. The communications device of claim 1, wherein the silencing frame istransmitted at beginning of the calculated transmission window.
 5. Thecommunications device of claim 1, wherein the transmission window iscalculated by adding a determined duration of the transmission window toa total duration of a next upcoming string of at least one higherpriority interval, and subtracting the sum of durations from end time ofthe last higher priority interval in the next upcoming string of atleast one higher priority interval to calculate a beginning time of thetransmission window.
 6. A communications device, comprising: atransceiver comprising at least two dissimilar wireless networktechnology subsystems, at least one subsystem of which is lower prioritythan at least another of the dissimilar subsystems, the transceiver ableto calculate a transmission window, and transmit a silencing frameduring a lower priority technology network interval during thetransmission window, wherein the silencing frame transmitted during thetransmission window silences devices for at least an entire duration ofstring of at least one higher priority network technology subsysteminterval.
 7. The communications device of claim 6, wherein thetransmission window is calculated by adding a plurality of transmissiontimes together to determine duration of the transmission window.
 8. Thecommunications device of claim 6, wherein the silencing frame istransmitted at beginning of the calculated transmission window.
 9. Thecommunications device of claim 6, wherein the transmission window iscalculated by adding a determined duration of the transmission window toa total duration of a next upcoming string of at least one higherpriority interval, and subtracting the sum of durations from end time ofthe last higher priority interval in the next upcoming string of atleast one higher priority interval to calculate a beginning time of thetransmission window.
 10. The communications device of claim 9, whereinthe silencing frame is transmitted at beginning of the calculatedtransmission window.
 11. A communications device, comprising: atransceiver comprising at least two dissimilar wireless networktechnology subsystems, at least one subsystem of which is lower prioritythan at least another of the dissimilar subsystems, the transceiver ableto calculate a transmission window, and transmit a silencing frameduring a lower priority technology network interval during thetransmission window, wherein if the silencing frame cannot betransmitted during the transmission window, no silencing frame is sentduring the lower priority technology network interval.
 12. Thecommunications device of claim 11, wherein the silencing frame istransmitted at beginning of the calculated transmission window.
 13. Acommunications device, comprising: a transceiver comprising at least twodissimilar wireless network technology subsystems, at least onesubsystem of which is lower priority than at least another of thedissimilar subsystems, the transceiver able to calculate a transmissionwindow, and transmit a silencing frame during a lower prioritytechnology network interval during the transmission window, wherein ifthe silencing frame cannot be transmitted during the transmissionwindow, no silencing frame is sent during the lower priority technologynetwork interval.
 14. The communications device of claim 13, wherein thetransmission window is calculated determining by adding a plurality oftransmission times together to determine duration of the transmissionwindow.
 15. The communications device of claim 14, wherein the silencingframe is transmitted at beginning of the calculated transmission window.16. The communications device of claim 13, wherein the silencing frameis transmitted at beginning of the calculated transmission window. 17.The communications device of claim 13, wherein the transmission windowis calculated by adding a determined duration of the transmission windowto a total duration of a next upcoming string of at least one higherpriority interval, and subtracting the sum of durations from end time ofthe last higher priority interval in the next upcoming string of atleast one higher priority interval to calculate a beginning time of thetransmission window.
 18. The communications device of claim 17, whereinthe silencing frame is transmitted at beginning of the calculatedtransmission window.